You can try that and see if there is a program that you can uninstall that you do not know what it does - google any you don't recognise.
If this had happened to me, I would, for "peace of mind", at least refomatt the hard disk and start from scratch.
Depending on the ability of the chap, he may have hidden his tracks very deeply.
I'd, in reality, replace the hard disk - they are very cheap these days.